I see from your profile it's a 91, and I'd guess it's a 4.0L pushrod engine with the DIS ignition. With the CEL light on, the ECA should have set a code, and that would be a good place to start. Last week I just read about the tach and ignition, but can't for the life of me remember what it said, and I can't find the info again. I believe you should have a tach signal during cranking, and that's your best clue for troubleshooting this. If you find the cause of the no-tach problem, I believe you'll have fixed your problem. Hope this little bit helps...